1. Field of the Invention
The present invention relates to a disconnectable thyristor and in particular to such a thyristor having a pnpn-layer sequence with a plurality of emitter parts and switching transistors disposed at the edges of the emitter parts.
2. Description of the Prior Art
In the field of power semiconductor devices it is known to quench a thyristor by subjecting the p-base, through an electrode, with a negative extraction current pulse generated by an external extraction current source. The negative extraction current pulse reduces the positive holes of the electron-hole plasma flooding the p-base and the n-base. Electrons of the plasma are then no longer compensated in a space-charge fashion, and must flow off to the anode of the thyristor. The plasma is initially decomposed in the vicinity of the electrode by means of which the current pulse is supplied, the plasma decomposition subsequently spreading to regions farther from the electrode beneath the n-emitter.
A disadvantage of such conventional quenching means is that the load current flowing through the thyristor, because of the relatively gradual reduction of the plasma, is initially only slightly decreased, with the result that the carrier density in the plasma is actually initially increased, counter to the desired result, i.e., extraction of the plasma. Therefore a sufficiently large extraction current pulse is required which may be, for example, up to 50 ampers in the case of a load current of 100 ampers. If the amplitude of the extraction current pulse necessary for plasma extraction is not attained, extraction of the plasma proceeds to a certain point and then remains at a standstill. The thyristor must then conduct a load current, which has not been significantly decreased, with the partially-extracted plasma, which may as a consequence destroy the thyristor.
A thyristor having controllable emitter-base short circuits which are actively connected for quenching the thyristor is described in German AS 2,945,324. This device does not, however, utilize an external extraction current source connected for the purpose of quenching the thyristor.